For the first time, preventive drugs are to be offered to women at risk of breast cancer under the NHS. The drugs, tamoxifen and raloxifene, were recommended by the National Institute for Health and Care Excellence (NICE), but accessing them could be difficult in Britain due to inadequate drug licensing laws. By relying on drug companies to push for extended licences for drugs, we are putting women and doctors in tricky positions when it comes to preventing cancer.
How do the drugs work?
Tamoxifen has been used to treat breast cancer for many decades. The observation in 1985 that it reduced new breast cancers in the opposite breast in women already being treated for breast cancer was the first evidence of its preventive properties. Raloxifene was first used to treat osteoporosis, but in 2001 it was found to also reduce breast cancer.
Several prevention trials have now been completed for both of these drugs and also for two other similar drugs. My colleagues and I recently published an overview of all of these trials. Overall, the drugs reduced breast cancer by 38% after ten years. The effects were seen only for one type of breast cancer: oestrogen receptor positive cancer.
Assessing risk
In one trial that directly compared the two drugs, tamoxifen was found to be more effective than raloxifene, but raloxifene produced fewer side effects. These side effects were an increase in blood clots and womb cancer.
Still, the side effects are generally less severe than having breast cancer. And to put this in perspective: if 1000 women at increased risk of breast cancer took tamoxifen for five years, there would be 22 fewer incidences of breast cancer among the group. By contrast, both blood clots and womb cancers would only increase by six. It’s clear, then, that the benefit to harm ratio is favourable for both drugs for most women.
The recommendations are to offer tamoxifen or raloxifene for five years to women at a high risk of breast cancer (a 30% lifetime risk) and to consider prescribing one of these drugs to women at moderately increased risk (a 17% to 30% lifetime risk). The lifetime risk of an average woman is estimated to be about 10%.
As there are about 8 million women in the UK aged 40-64, this equates to about 90,000 high-risk women and another 720,000 moderately high risk women who would be eligible for preventive therapy.
License to prevent
This should all be good news, but some issues remain. Both of these drugs have been approved for breast cancer prevention by regulatory authorities in the United States, but not in Britain. Because the drugs are currently produced for one purpose - to treat, not prevent, breast cancer in the case of tamoxifen and to treat osteoporosis in the case of raloxifene - they need to be approved specifically for their new purpose.
Only a drug manufacturer can apply to extend a drug’s license, and as the drugs are now “off-patent” and can be produced generically by other companies, there is little incentive for a company to go through the complicated and expensive process of doing so.
So in the UK, a doctor must still be held personally responsible for prescribing the drugs in their new role. This will be a disincentive for widespread use.
This problem will become an increasingly important issue as new uses of many drugs that are now out of patent are being found. We are currently researching another drug that is even more effective than tamoxifen and raloxifene in preventing breast cancers. But it will face the same licensing issues unless something is done.
A solution would be for the UK licensing authority to accept an independent review from NICE as the basis for extending the license of drugs approved for other purposes. This will probably require new legislation, but a solution of this sort is clearly in the public interest. As we improve our understanding of breast cancer, it’s important that drug licensers keep up.